1. Field of the Invention
The present invention relates generally to a device for conveying long articles within heat treatment furnaces, and more particularly to the application of such conveyance devices to heat treatment furnaces for imparting a continuous bright annealing treatment to metal pipes and tubes, such as for example, nuclear fuel clad stainless tubes utilized within nuclear power generation plants, for which bright annealing treatment is essential and/or desirable.
2. Description of the Prior Art
Bright annealing treatment, utilizing helium, argon, hydrogen or ammonia gas, is frequently applied to metal products, such as, for example, wire, pipe, and the like, made of zirconium and its alloys, nickel and its alloys, stainless steel, and similar metals. For especially high-grade precision pipes, such as, for example, nuclear fuel clad tubes to be utilized within nuclear power generating plants, bright annealing treatment, as at least the final annealing treatment, is a necessity due to the fact that the bright annealing treatment eliminates the adhesion of fluorides and chlorides to the pipes, which occur during descaling, whereby picking and washing processes become unnecessary. Bright annealing therefore offers the advantages of permitting continuous processing, and achieving product surface conditions which are closest to the final polished state.
When performing bright annealing treatment upon nuclear fuel clad stainless tubes or similar tubes and pipes, the treatment must not produce any flaws within the product, nor cause any precipitation of chromium carbide during cooling of the product. There exists a strict standard for nuclear fuel clad stainless tubes which requires that surface flaws should not exceed 25 .mu. and that there should be a minimum precipitation of chromium carbide. Nevertheless, within conventional devices employed for the conveyance of long articles within bright annealing furnaces, it is difficult to obtain good results, flaws often being produced upon the external surface of the product, chromium carbide precipitation is detected, and changes in the grain size of austenite phases within the metal also occur.
In addition, the mesh belt utilized within these product conveyance devices frequently becomes elongated thereby becoming unevenly wound about the driving part of the device.